June 20, 2007 — People who receive information about treatment outcomes expressed by physicians in terms of number needed to treat consent to various recommended interventions, according to the results of a cross-sectional survey published in the June 19 issue of the Annals of Internal Medicine.
"How physicians communicate the risks and benefits of medical care may influence patient's choices," write Peder A. Halvorsen, MD, from the University of Southern Denmark in Odense, and colleagues. "Ways to communicate the benefits of risk-reducing drug therapies include the number needed to treat (NNT) to prevent adverse events, such as heart attacks or hip fractures, and gains in disease-free life expectancy or postponement of adverse events. Previous studies suggest that the magnitude of the NNT does not affect a layperson's decision about risk-reducing interventions, but postponement of an adverse event does affect such decisions."
The investigators surveyed the general community, presenting scenarios regarding a hypothetical drug therapy to reduce the risk for heart attacks (1754 respondents) or hip fractures (1000 respondents). For both scenarios, the data sources were clinical trials.
Respondents were randomized to a scenario with 1 of 3 outcomes after 5 years of treatment. For the drug to prevent heart attacks, the outcomes were postponement by 2 months for all patients, postponement by 8 months for 1 of 4 patients, or an NNT of 13 patients to prevent 1 heart attack.
For the drug to prevent hip fractures, the outcomes were postponement by 16 days for all patients, postponement by 16 months for 3 of 100 patients, or an NNT of 57 patients to prevent 1 fracture. Study endpoints were consent to receive the intervention and perceived ease of understanding the treatment effect.
The overall rate of response to the survey was 81%. In the heart attack scenarios, consent for drug therapy was given by 93% of respondents who were presented with the NNT outcome, 82% of those who were presented with the outcome of large postponement for some patients, and 69% of those who were presented with the outcome of short postponement for all patients (χ2, 89.6; P < .001).
For the hip fracture scenarios, corresponding consent rates were 74%, 56%, and 34%, respectively (χ2, 91.5; P < .001). Respondents who reported understanding the treatment effect were more likely to consent to therapy.
Study limitations were that decisions were based on hypothetical scenarios, not real clinical encounters; only 61% of invited persons attended the screening; the survey questionnaire did not probe deeply into respondents' understanding of the scenarios; and the scenarios were not tailored to the individual respondents' level of risk.
"Treatment effects expressed in terms of NNT yielded higher consent rates than did those expressed as equivalent postponements," the authors write. "This result suggests that the description of the anticipated outcome may influence the patient's willingness to accept a recommended intervention."
The University of Tromso in Norway supported this study. The authors have disclosed no relevant financial relationships.
"Halvorsen and colleagues' findings are welcome because they remind us about framing effects and show how they could affect decisions about preventative interventions," Harold C. Sox, MD, editor of the Annals of Internal Medicine, writes in an accompanying editorial. "They show that it is hard to communicate the risk for events realistically and without biasing our patients. Hopefully, this reminder will stimulate researchers, medical students, and practicing physicians."
Dr. Sox has disclosed being a director of the Foundation for Informed Medical Decision Making, which reimburses some of his travel expenses.
Ann Intern Med. 2007;146:848-856, 891-892.
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